1. Technical Field
The present invention relates to an optical touch system and an object coordination data calculation method thereof.
2. Related Art
Touch screen devices allow users to interact directly on screen with application programs. One of the more common types of touch screen devices is the optical touch screen device.
FIG. 1 shows a current optical touch screen system 1 disclosed in U.S. Pat. No. 4,782,328. As shown in FIG. 1, the optical touch screen system 1 comprises two image sensors 11 configured to capture the image of an object 13 on a touch screen 12. The processor 14 coupled with the two image sensor 11 processes the images from the two image sensors 11 to decide the sensing paths 15 respectively connecting the object 13 and the two image sensors 11. The processor 14 calculates the coordinates of the object 13 using the sensing paths 15. The optical touch screen system 1 needs two image sensors 11, making it expensive.
FIG. 2 shows another current optical touch screen system 2. U.S. Pat. No. 7,689,381 B2 (or counterpart Taiwan Publication Patent No. 201003477) discloses an optical touch screen system 2 targeted at reducing cost of production. The optical touch screen system 2 comprises a mirror 21, two light sources 22, an image sensor 23, and a processor 24. The mirror 21 and the two light sources 22 are disposed at the periphery of a touch area. The mirror 21 is configured to generate a reflection 26 of an object 25. The image sensor 23 is configured to generate an image of the object 25 and an image of the reflection 26. The processor 24 determines a sensing path 27 passing through the image of the object 25 and another sensing path 27 passing through the image of the reflection 26, and then calculates the coordinates of the object 25 using the two sensing paths 27. The optical touch screen system 2 needs only one image sensor 23, making it relatively cost effective.
In the optical touch screen system 2, the image of the object 25 and the image of the reflection 26 may overlap when the two sensing paths 27 get too close to each other, in which case the position of the object 25 cannot be calculated. To address this problem, U.S. Patent Publication No. 2010/0090950 A1 (or counterpart Taiwan Publication Patent No. 201101131) discloses a calculation method. The calculation method utilizes the image of the object 25 and a predetermined dimension of the object 25 to calculate the coordinates of the object 25 when the image of the object 25 and the image of the reflection 26 overlap. In the calculation method, the orthographic projection of the object 25 on the touch area is assumed as a circular projection whose radius is used as the above predetermined dimension. However, users may use fingers or other soft objects to operate the optical touch screen system, and such types of object cannot always create a fixed predetermined dimension. As a result, errors may occur in coordinate data calculation.